Surgical and medical management in the treatment of proximal tibial metaphyseal fracture in immature dogs

The purpose of this study was to report approaches to surgical and medical management of proximal tibial metaphyseal fractures (PTMF) and short-term case outcome. Medical records of immature dogs with PTMF were reviewed and data were collected including history, signalment and side affected. Data pertaining to surgical and medical management including radiographic evaluation and short-term complications were recorded. Forty-five dogs with a total of 47 PTMF identified and treated between 2007–2019 were included in this study. Six cases were managed with external coaptation alone. Forty-one cases were treated surgically with constructs including K-wires in different configurations, bone plate and screws, and external skeletal fixation. Of the cases managed conservatively, 4 developed complications, including bandage sores, diffuse osteopenia of the tarsus/metatarsus, and angular limb deformities. Surgical complications including pin migration necessitating removal, osteopenia, and screw placement in the proximal tibial growth plate or into the stifle joint were found in 16 cases. PTMF treated with surgery had a subjectively more predictable outcome compared to those treated with external coaptation alone. Conservative management may result in complications including development of excessive tibial plateau angle (TPA) as well as distal tibial valgus.


Introduction
Tibial fractures account for approximately 20% of all long bone fractures in companion animals, making them the third most commonly occurring fracture [1,2]. Fractures involving the proximal tibial metaphysis are relatively uncommon, and are reported to comprise 3.7% of all tibial fractures [3]. Other fractures of the proximal tibia include tibial tuberosity avulsion fractures, Salter Harris Type II fractures, and combined tibial tuberosity avulsion and proximal physeal fractures [4,5]. Until recently, it had been suggested that fractures of the proximal tibial metaphysis were exclusive to mature animals secondary to severe trauma [6][7][8]. However, Deahl et al. reported the occurrence of proximal tibial metaphyseal fractures (PTMF) in juvenile dogs (mean age 4.6 months) following minimal trauma [9]. Most commonly, PTMF manifest in a characteristic curvilinear configuration (Fig 1). The authors of that study suggested that the transition from diaphyseal to metaphyseal bone and the immature or transition zone of the metaphysis play a role in the development of this fracture configuration [9].
In most reported proximal metaphyseal tibia fractures, craniomedial displacement of the distal tibia fragment relative to the proximal fragment occurs. This results in caudolateral angulation of the distal limb. The cranial displacement of the distal fragment and caudal tipping of the proximal tibia increases the risk for development of a steep tibial plateau angle and therefore increased strain on the cranial cruciate ligament as it heals (Fig 2) [10]. In the frontal plane, these fractures may also result in valgus angulation in the distal fragment ( Fig 3C).
Clinical outcomes for dogs following management of PTMF have not been reported in the literature. Treatment options for stabilization of these fractures are influenced by multiple factors, including patient age, the presence of open physes, degree of fragment displacement, availability of proximal metaphyseal bone stock, and cost to the client.
The objective of this study was to report on surgical and conservative approaches to the management of PTMF, including complications and short-term outcome.

Study design
Medical records of dogs that presented with a PTMF between the years of 2015-2020 were collected from several veterinary referral hospitals. Data retrieved from the medical records included breed, weight, side affected, age at the time of presentation, gender, sterilization status at the time of the injury, details of the inciting trauma, displacement, presence of concurrent fibular fracture, stabilization technique (external coaptation vs. surgical fixation) and recorded complications.

Results
Forty-seven fractures occurring in 45 dogs were available for review (Table 1).

Laterality
The right tibia was affected in 17 cases and the left tibia was affected in 22 cases. Two cases were bilaterally affected. Four cases were lacking information regarding laterality.

Fracture causes
In all but three cases, the reported cause of the fracture was a fall or jump from a low height, which was consistent with reported causes described in Deahl et al. [9] The medical records for the remaining three cases did not contain information regarding inciting cause.

Concurrent fibular fracture
Concurrent fibular fracture occurred in 33 of the 46 cases with mediolateral and craniocaudal radiographs available. Of those managed with external coaptation alone, 3 cases had a concurrent fibular fracture and 2 had intact fibulae. Access to only one radiographic view of one medically managed case made it challenging to determine whether a fibular fracture was present. Of the cases managed surgically, 30 sustained fibular fractures and 12 did not have a fibular fracture.

Fracture treatment
Of the 47 fractures available for review, 6 were treated non-surgically with external coaptation consisting of a bandage and splint for a mean period of 5 weeks (Table 1).
Forty-one fractures were treated surgically. Fracture stabilization using K-wires was performed in 26 cases, 23 of which were repaired with a cross-pinning technique, and 3 of which were repaired with pins and a tension band wire. A soft padded bandage or cranial splint was applied in 9 of these cases for a mean of 17.2 days postoperatively. In 14 cases, stabilization was performed using a bone plate and screws (Table 1). Plates applied included a non-locking Tplate (5), locking T-plate (7) (Fig 4), locking L-plate (1), non-locking L-plate (1), locking TPLO plate (1) (Fig 5), and a dynamic compression plate (1). Two of the plated cases were treated with either a soft padded bandage or lateral splint for a mean of 17.5 days postoperatively. One case was treated with an intramedullary pin and modified type 1a external fixator for 8 weeks (Fig 6).

Complications
Of the 6 cases managed with external coaptation alone, 4 developed complications. Following the development of genu varum, medial patellar luxation, tibial tuberosity avulsion fracture, patella alta, tarsal osteopenia, and fibular malunion after 6 weeks of management in a cranial splint (Fig 3), one patient ultimately underwent amputation of the left pelvic limb (case 34). One bilaterally affected case developed internal tibial rotation and excessive TPA with bilateral medial patellar luxation and diffuse osteopenia of the tarsus and metatarsus. The patellar luxations ultimately required surgical correction (case 40, Fig 7). The remaining case developed bandage sores and disuse osteopenia that resolved following bandage removal (case 45). Complications were recorded in 9 cases that underwent surgical repair using pins or pins and tension band wire. Pin migration or breakage was the most common complication and occurred in 6 cases (cases 12, 21, 28, 29, 33, and 35) all of which required a second surgery to either replace or remove the displaced implants. In one case (case 37a and b), external coaptation was used as repair augmentation (3 weeks of a cranial splint followed by 1 week of modified Robert Jones bandage). This resulted in development of diffuse osteopenia of the tarsus and metatarsus, which improved following bandage removal (Fig 8). The remaining pin construct case with a complication was continued to exhibit an intermittent lameness at the time of the last follow-up 8 weeks after surgery. In this case it was noted that the patella rode along the medial trochlear ridge but could not be luxated (case 32).
Seven cases that underwent internal fixation using a plate and screws developed complications. The most proximal screw passed through the proximal tibial physis and was left in place (case 6 (Fig 9), 11, and 41 ( Fig 10). This resulted in development of a valgus deformity at the fracture site in 2 cases (case 6 and 11). There was no apparent dysfunction of the limb during follow-up. In two cases, a screw violated the proximal tibial physis and penetrated the stifle   15 and 17, Fig 11). One case was lost to follow up and the other recovered well without any reported lameness. The remaining two cases treated with plate and screw fixation developed surgical site infections that resolved with either implant removal 12 weeks after surgery or oral antibiotic therapy (case 10 and 27, respectively).

Discussion
Both surgical and conservative approaches to the management of proximal tibial metaphyseal fractures have been described. Clinically, patients treated with surgical stabilization appeared to have superior outcomes compared to those treated with external coaptation alone. However, the small sample size of the present study precludes the demonstration of statistical significance. Despite the small sample site, the authors believe there is evidence to suggest that surgical stabilization of these cases achieves better clinical outcome with a lower risk of severe complications compared to use of external coaptation alone. Fracture of the proximal tibial metaphysis typically occurs in juvenile dogs [6], and the use of external coaptation during periods of sustained growth may result in complications including angular limb deformity, muscle contracture, and/or disuse osteopenia [11]. Additionally, bandages may also contribute to the development of sores, swelling, and dermatitis [12]. One patient in this study required amputation of the affected limb as a direct result of complications arising from external coaptation. Given the potential for significant complications, the authors believe external coaptation alone should only be considered for cases in which limited financial resources make surgical correction impossible.
Of the fractures that underwent primary surgical repair, 26 were stabilized using a pin construct, 14 were stabilized using a bone plate and screws and one was stabilized with a type 1a external fixator. Regardless of stabilization method, all surgical cases had a more predictable outcome when compared to the cases managed with external coaptation alone.
Internal fixation constructs using pins included cross pinning, multiple diverging K-wires and intramedullary pin placement. The most common complication encountered in these cases was pin migration, often necessitating removal following documentation of adequate fracture healing. Three previous studies on fracture pinning showed a variable pin removal rate after reduction of physeal fractures. Boekhout-Ta et al. reported a pin migration rate of 4% and elective pin removal due to irritation was performed in 41% of cases in this study [13]. In 2004, it was reported that no pins migrated or were removed in 7 young dogs undergoing open reduction and internal fixation of proximal tibial fractures [14]. Another study in 1989 evaluated blind pinning of the tibia and femur in dogs. There was a 71% pin removal rate reported in 7 physeal fractures [15]. At this time, more information is needed regarding pin migration rate and removal for cases of PTMF, although removal is considered standard of care if migration or irritation occurs.

PLOS ONE
Treatment of proximal tibial metaphyseal fracture in young dogs Subjectively, we appreciated an increased difficulty associated with reduction of the fracture site during surgery when pins were used. Interestingly, even in dogs that underwent primary repair with pins, bandages appeared to increase the risk of complications, though the significance of this finding could not be demonstrated due to low case numbers. However, the use of external coaptation following repair of PTMF with pins should be approached cautiously. It is recommended to closely follow up on cases that were repaired with pins both clinically and radiographically in order to address any complications such as pin migration and soft tissue mobility.
The most common complication encountered in the cases managed with a bone plate and screws was inadvertent placement of the most proximal screw through the proximal tibial physis. This resulted in valgus deviation of the proximal tibia in 2 cases (Fig 9), but did not affect the clinical outcome of these patients in the short-term. Long-term follow up would be necessary to fully determine whether this change is clinically significant. One case with physeal violation continued grow normally and did not develop distal tibial valgus (case 41, Fig 10). Kennon et al. described that limited central transphyseal bridging that occurs after physeal injury can be associated with continued normal hydrostatic bone growth to overcome physeal violation, which may explain the outcome of this case [16]. In two cases, the proximal screw violated the proximal tibial physis and penetrated the stifle joint. It is likely that the use of intraoperative fluoroscopy would greatly diminish the risk of this complication. There is no

PLOS ONE
Treatment of proximal tibial metaphyseal fracture in young dogs indication in the medical records as to why these cases were not immediately re-operated to achieve appropriate screw placement. Possible reasons for this may be due to limited bone stock in these small patients, the potential for destabilization of the construct, or planned future removal of the implants once the fracture healed. When fluoroscopy is not available, particular care should be taken to evaluate the placement of the proximal screw on postoperative radiographs. If violation of the proximal tibial physis or the articular surface is apparent, revision should be undertaken prior to recovering the patient.
Intraarticular screw placement causes chondral damage, exacerbates chondrolysis and osteoarthritis, and therefore should be avoided [17]. In the two cases with penetration of the proximal screw into the stifle joint, both patients recovered well and did not have any clinical  There was concern for collapsing of the lateral tibial cortex resulting in increased tibial angulation. The patient was still grade 4/4 lame on exam, so surgical stabilization was elected. E and F: Mediolateral and craniocaudal views immediately postoperatively showing screw placement into the joint. G and H: Mediolateral and craniocaudal views performed 6 weeks postoperatively with screw placement still within the joint, but patient was not lame or painful on exam. lameness at the time of last follow-up. It is possible that the lack of apparent pain or lameness in these cases is due to skiving, which is defined in human literature as the condition when the subchondral plate is disrupted while the underlying cartilage is physically displaced without the screw entering the joint [18]. CT scan has a greater sensitivity compared to radiography when diagnosing skiving, which was not performed in any of the cases in this study [18]. It is possible that these cases had skiving as opposed to intraarticular screw violation, which accounts for the favorable outcome in both patients.
One case was managed with an intramedullary pin and type 1a external fixator (Fig 5) and recovered well without any noted complications. This type of fracture fixation method may be useful for PTMF given the limited bone stock of the proximal fracture fragment, its proximity to the proximal tibial physis and the potential for rapid healing due to patient age [19].
Of particular concern in canine PTMF is the cranial displacement of the distal segment, which results in caudal tipping of the proximal tibia and risks the development of an excessive tibial plateau angle, potentially increasing strain on the cranial cruciate ligament (Figs 2 and 7) [10]. Surgical intervention allows for more accurate reduction of the fracture fragments, therefore reducing the risk of caudal tipping of the proximal segment. None of the patients in this study developed cranial cruciate ligament rupture, but this may be attributed to the short-term follow-up. We also recognized that PTMF configuration may result in distal tibial valgus. This may also be corrected by the superior reduction and alignment afforded by surgical intervention as opposed to medical management with external coaptation.
Limitations of this study include those inherent to its retrospective nature, a low number of cases that precluded statistical analysis between and within the various groups, inconsistent methods of surgical stabilization employed, inconsistent use of postoperative bandages and splints, and a lack of consistency of radiographic evaluation among the cases reviewed. Further studies are needed to determine the most effective method of surgical intervention for fracture repair.
Despite limitations within this study, we reported surgical and medical management of PTMF fractures along with the short-term outcome. Subjectively, surgical management has a more predictable outcome and can prevent conformational changes to the proximal tibia that may predispose patients to cranial cruciate ligament rupture and angular limb deformity.